Question

Help creating Java Applet

Asked by: P1ST0LPETE

Hi,
I'm fairly new to Java, took a few classes in college, but haven't touched it in years, and now I need to add a Java Applet to a .Net web application. I have the following java code (shown in code snippet) to get the MAC address of the client.

From the example I found online, it looks like JavaScript is used to call the Java Applet. However, the java applet that is being called in the example has a file extension of .jar. When I go into my project folder (I'm using NetBeans btw, just downloaded the IDE today) my class file has the file extention of .java. I'm getting ready to try to test the applet, will it matter if the file ends in .jar or .java? If it does matter, I guess I'm not compiling it correctly, but i'm not sure what I'm not doing.

Also, once I have the MAC address held in the java applet, how do I pass that to JavaScript?

import java.applet.Applet;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class ClientAuthentication extends Applet
{
    public void init()
    {
        try
        {
            String mac = this.getMacAddress();
            System.out.println(mac);
        }
        catch(Exception ex)
        {
            System.out.println(ex);
        }
    }
 
    private String getMacAddress() throws IOException
    {
        String mac = null;
        String command = "ipconfig /all";
        Process process = Runtime.getRuntime().exec(command);
        BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
        while (true)
        {
            String line = reader.readLine();
            if(line == null) { break; }
            Pattern pattern = Pattern.compile(",*((:?[0-9a-f]{2}[-:]){5}[0-9a-f]{2}).*", Pattern.CASE_INSENSITIVE);
            Matcher matcher = pattern.matcher(line);
            if(matcher.matches())
            {
                mac = matcher.group(1);
                break;
            }
        }
        reader.close();
        return mac;
    }
}

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Asked On: 2009-10-29 at 13:08:22ID24856094
Topics: JavaScript
,; New to Java Programming
,; Java Programming Language
Participating Experts: 2
Points: 500
Comments: 21

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Answers

by: CEHJPosted on 2009-10-29 at 13:38:50ID: 25697997

No - it doesn't matter that it's either in a jar or not. What does matter is that the method you want to call from JavaScript be public. You'll need to change that from its current private

by: objectsPosted on 2009-10-29 at 14:39:45ID: 25698540

jar and java files are different.
.java are the source java files
when compiled they produce .class files (byte code)
class files can then be packaged in a .jar file which is basically just a zip file containing classes and resources.

by: objectsPosted on 2009-10-29 at 14:42:58ID: 25698571

And it does matter whether you use a .jar file or not as you need to change the html to tell it where it needs to load the byte code from.
And you wouldn't use the .java file to run the applet, you would either use the .class file or create a .jar file containing the class file

ie. its not just a matter of changing the file extension

some background

http://java.sun.com/docs/books/tutorial/deployment/applet/

by: objectsPosted on 2009-10-29 at 14:44:16ID: 25698577

actually you will have to create a jar file for that applet to run as it needs to be signed.

http://java.sun.com/developer/onlineTraining/Programming/JDCBook/signed.html

by: P1ST0LPETEPosted on 2009-10-30 at 09:56:55ID: 25704839

Thanks for the replies, this is helping quite a bit.

On Sun's tutorials, I see the following JavaScript code for launching an applet:

<script src="http://www.java.com/js/deployJava.js"></script>
<script>

var attributes = { id:'mathApplet', code:'jstojava.MathApplet', width:1, height:1} ;
var parameters = {jnlp_href: 'math-applet.jnlp'} ;
deployJava.runApplet(attributes, parameters, '1.6');
</script>

Is that first line (i.e. <script src="http://www.java.com/js/deployJava.js"></script>) required in order for the applet to deploy properly?

Also, do I need a "main class" for a java applet?

by: CEHJPosted on 2009-10-30 at 10:04:59ID: 25704909

>>Is that first line ...

Yes, if you want to use that particular script

>>Also, do I need a "main class" for a java applet?

No

by: P1ST0LPETEPosted on 2009-10-30 at 12:02:37ID: 25705901

Ok, I have a little test app with the following code: (see snippet below)

When I click the button, the alert() fires off showing the javascript is running, then I get an error in visual studio saying: "Microsoft JScript runtime error: Object doesn't support this property or method" the "document.JavaClient.getMacAddress();" line is highlighted.

What am I doing wrong?

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Test App</title>
    <script type="text/javascript">
        function AuthenticateClient()
        {
            alert("Hello");
            document.JavaClient.getMacAddress();
        }
    </script>
</head>
<body>
<form id="form1" runat="server">
    <div>
        <asp:Button ID="TestButton" runat="server" Text="Test Java App" OnClientClick="AuthenticateClient()" /> 
    </div>
    <br />
    <applet name="JavaClient" code="Java/ClientAuthentication.class"  height="20" width="100"></applet>
</form>
</body>
</html>

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by: CEHJPosted on 2009-10-30 at 13:04:25ID: 25706351

Try

<applet id="JavaClient" name="JavaClient" code="Java/ClientAuthentication.class" height="20" width="100"></applet>

by: P1ST0LPETEPosted on 2009-10-30 at 13:42:55ID: 25706638

Ok, made a few changes (see below), and visual studio is throwing an error on the "document.JavaClient.getMacAddress()" line of code, but the error is different:

Java: java.security.AccessControlException: access denied (java.io.FilePermission <<ALL FILES>> execute)

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Test App</title>
    <script type="text/javascript">
        function AuthenticateClient()
        {
            alert("Hello");
            document.JavaClient.getMacAddress();
        }
    </script>
</head>
<body>
<form id="form1" runat="server">
    <div>
        <asp:Button ID="TestButton" runat="server" Text="Test Java App" OnClientClick="AuthenticateClient()" /> 
    </div>
    <br />
    <applet id="JavaClient" name="JavaClient" archive="Java/ClientAuthentication.jar" code="AuthenticateClient.class"  height="20" width="100"></applet>
</form>
</body>
</html>

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by: P1ST0LPETEPosted on 2009-10-30 at 13:44:38ID: 25706649

Is that error being thrown due to what Savant said earlier?

"actually you will have to create a jar file for that applet to run as it needs to be signed."

by: CEHJPosted on 2009-10-30 at 13:46:16ID: 25706667

Yes - you need to sign the applet

http://www.brendonwilson.com/projects/signed-java/

by: P1ST0LPETEPosted on 2009-11-02 at 07:02:42ID: 25719952

Ok, so I've gone through a few tutorials explaining how to sign a java applet. All of them describe using commands from the DOS prompt such as "keytool" and "jarsigner". What do I need to setup to enable myself to use these command prompt commands, because when I try to use them I get an error saying: " 'keytool' is not recognized as an internal or external command, operable program or batch file. "

by: CEHJPosted on 2009-11-02 at 07:04:20ID: 25719967

You need to make sure the JDK (not JRE) bin directory is in your PATH

by: P1ST0LPETEPosted on 2009-11-02 at 10:21:57ID: 25722032

Ok, I got a certificate made and the applet signed using the jarsigner functionality.
Tested (in IE8) and was met with a java popup, alerting me that the website I was viewing had a signed application attempting to run, and asking me if I wanted to allow it. I accepted "yes", to allow my code to run and then clicked the button to test the code. Upon click the button, I got the same results as above. The JavaScript alert would fire saying "Hello", and then I would get an error in Visual Studio, and the following line:

document.JavaClient.getMacAddress();

would be highlighted yellow and giving the following error message:

Java: java.security.AccessControlException: access denied (java.io.FilePermission <<ALL FILES>> execute)

So, exact same result as before when the applet wasn't yet signed.
Also, when I was prompted by Java to determine if I wanted to allow the applet to run or not, I clicked a little checkbox, that said "always allow this applet to run". How can I un-check that, so that I am prompted to allow the applet to run each time I load the page (this is for testing purposes).

by: CEHJPosted on 2009-11-02 at 11:01:14ID: 25722460

Sounds like it might be improperly signed. *All* jars need to be signed btw.

Make sure your applet cache is emptied and it should prompt you each time afaik

by: objectsPosted on 2009-11-02 at 13:20:58ID: 25723870

now that you have signed the applet as I suggested earlier the next step is to run the code in a privileged block

http://helpdesk.objects.com.au/java/my-signed-applet-is-throwing-an-accesscontrolexception

by: P1ST0LPETEPosted on 2009-11-03 at 11:49:05ID: 25732762

Ok, I'm working on trying to get the privileged block to work.
I'm getting hung up with the following code:

AccessController.doPrivileged(new PrivilegedAction()
{
public Object run()
{
return null;
}
});

I'm getting the following error:

cannot find symbol
symbol: variable AccessController
location: class ClientAuthentication
internal error; cannot instantiate () at <anonymous PrivilegedAction> to ()

by: objectsPosted on 2009-11-03 at 14:47:53ID: 25734744

you need to import it

import java.security.AccessController;

by: P1ST0LPETEPosted on 2009-11-04 at 06:42:15ID: 25739723

"you need to import it - import java.security.AccessController;"

I actually tried that as soon as I got the error, and it still didn't fix the problem. Current code looks like this:

import java.applet.Applet;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.security.AccessController;
 
public class AuthenticateClient extends Applet
{
    public void init()
    {
 
    }
 
    public void getMacAddress() throws IOException
    {
        try
        {
            AccessController.doPrivileged(new PrivilegedAction()
            {
               public Object run()
               {
                   return null;
               }
            });
            String mac = "";
            String command = "ipconfig /all";
            Process process = Runtime.getRuntime().exec(command);
            BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
            while (true)
            {
                String line = reader.readLine();
                if(line == null) { break; }
                Pattern pattern = Pattern.compile(",*((:?[0-9a-f]{2}[-:]){5}[0-9a-f]{2}).*", Pattern.CASE_INSENSITIVE);
                Matcher matcher = pattern.matcher(line);
                if(matcher.matches())
                {
                    mac = matcher.group(1);
                    break;
                }
            }
            reader.close();
            System.out.println(mac);
        }
        catch(Exception ex)
        {
            System.out.println(ex);
        }
    }
}

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by: objectsPosted on 2009-11-04 at 13:10:21ID: 25743984

you aren't importing PrivilegedAction

import java.security.PrivilegedAction;

by: CEHJPosted on 2009-11-23 at 12:41:42ID: 25891344

:-)

20120131-EE-VQP-002

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Help creating Java Applet

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